The present invention relates to a method for manufacturing a magnetic recording medium, and more particularly to a method for manufacturing a magnetic recording medium formed of a flexible strip-like support coated with a magnetic coating liquid.
In a general method for manufacturing magnetic recording media, for example, magnetic tape such as audio tapes and video tapes, and magnetic disks such as floppy disks, a flexible strip-like support, wider than the final product, is coated with a magnetic coating liquid, thereby to form a magnetic layer on the support. The magnetic layer thus formed is magnetically oriented and dried. The surface of the magnetic layer is smoothed to form raw film. The raw film is then cut into strips of a predetermined final-product width, or into a predetermined shape.
Various plastic web-like supports made of synthetic resins have been used in manufacturing magnetic recording media, for example, polyesters (e.g., polyethylene terephthalate and polyethylene-2,6-naphthalate), polyolefins (e.g., polyethylene and polypropylene), cellulose derivatives (e.g., cellulose acetate, cellulose diacetate, cellulose acetate butyrate and cellulose acetate propionate), polycarbonates modified with vinyl resins such as polyvinyl chloride and polyvinylidene chloride, polyimide, polyetherimide, polyamideimide, and the like.
With the recent trend of reducing the size of and increasing the recording density of magnetic record media, the web has become necessarily thinner. Therefore, the web is fragile and tends to be more readily deformed. Magnetic tapes formed using such fragile webs are apt to suffer from skewing, decreased output level, change of playback frequency, curling, and the like, particularly under high temperature conditions. As a result, the running of the magnetic tape tends to easily become abnormal.
Methods for manufacturing magnetic recording media capable of manufacturing magnetic recording media substantially free from deformation and curling of the recording media due to thermal contraction under high temperature conditions are disclosed for example, in Japanese Patent Laid-Open Publications Nos. Sho. 64-14725, Hei. 1-109520, Hei. 1-109528, and Hei. 1-109529. In such methods, a running web is coated with a magnetic coating liquid, thereby to form a magnetic layer thereover. The web, under a tension of 2 to 5 kg/m, is subjected to a heating/wetting process under a temperature of 80.degree. to 120.degree. C. and a relative humidity of approximately 60%.
In such a manufacturing method, however, if the tension acting on the web exceeds 5 kg/m in the heating/wetting process, slippage in the longitudinal direction can occur between the web and the magnetic layer. This slippage can cause the magnetic layer to crack. For this reason, the tension acting on the web had to be held below 5 kg/m.
With such restrictions, during the successive coating and heating/wetting processes, coating of the magnetic layer is performed at a high speed (e.g., a web transfer speed of 200 to 600 m/min) so that the web tension can be held below 5 kg/m. In this case, since the tension is weak, the web is apt to travel in a zigzag fashion. As a consequence, the web tends to wrinkle or be improperly taken up. This hinders high speed magnetic-layer coating, and hence a further improvement of production efficiency.